Dialysis, including hemodialysis and peritoneal dialysis, is a treatment mode for patients that suffer from inadequate kidney function. In hemodialysis, blood is pumped from the patient's body through an extracorporeal artificial kidney (dialyzer) circuit, where blood-borne toxins and excess water are filtered out of the blood through a semipermeable membrane into an electrolyte (dialysate) medium. A commonly used form of dialyzer comprises a large number of semipermeable hollow fiber membranes, which greatly increase the surface area available for dialysis to facilitate diffusion and convection across the membranes.
Existing dialysis systems typically consist of two parts; one comprising an extracorporeal blood flow circuit and the other comprising a dialysate circuit or flow path. Typically, the entire blood flow circuit is disposable and comprises: 1) an arterial and venous fistula needle, 2) an arterial (inflow) and venous (outflow) tubing set, 3) a dialyzer, 4) physiologic priming solution (saline) with infusion set, and 5) an anticoagulant, such as heparin or sodium citrate with infusion set. The arterial needle accesses blood from the patient's blood access site and is connected to the arterial blood tubing set, which conveys blood to the dialyzer.
The arterial line typically comprises: a pumping segment with interfaces to a rotary or peristaltic blood pump on the hemodialysis machine, pressure monitoring chambers including tubing which interfaces to pressure transducers on the machine to monitor the pressure pre-pump and/or post pump, inlet ports for saline and anticoagulant, and one or more injection sites for drawing blood or injecting drugs.
The dialyzer itself typically comprises a case which encloses a bundle of hollow fibers having a semi-permeable membrane. The blood is circulated on the inside of the hollow fibers while dialysis solution is circulated on the outside, so that the two never come into direct contact. Toxins diffuse out of the blood and into the dialysis solution owing to the concentration gradient. Excess water in the patient's blood enters the dialysate as a result of a pressure gradient. The membrane is made from cellulosic derivatives or synthetic polymers.
The venous line and needle carry the newly dialyzed blood away from the dialyzer and back into the patient's circulatory system. The venous set is comprised of a pressure monitoring chamber with tubing leading to another pressure transducer in the machine, injection sites, and a segment of tubing which interfaces to an air detection assembly in the machine in order to prevent air emboli from passing to the patient.
Dialysis solution is typically prepared continuously on-line in present-day machines by combining water which has first been purified by a separate water treatment system and liquid concentrates of electrolytes. Over the past decade the dialysate concentrates have evolved from a single formulation which contained acetate as the physiologic buffering agent for the correction of circulatory acidosis, to two containers where bicarbonate replaces acetate as the buffering agent. Two proportioning pumps are required, the first to mix the bicarbonate concentrate with water and the second to proportion this mixture with the concentrated electrolytes to achieve the final, physiologically compatible solution.
Most contemporary hemodialysis machines continuously monitor the pressure at the blood outlet side of the dialyzer by way of the pressure transducers connected to the blood sets and also in the dialysate circuit. Microprocessors calculate an estimated transmembrane pressure (TMP) which correlates to the amount of water transmission through the membrane. These machines may also have means of measuring the amount of dialysis solution entering and leaving the dialyzer, which allows the calculation of net water removal by ultrafiltration from the patient. By electronically comparing the amount of water entering or leaving the blood with the transmembrane pressure, the system is able to control actively the water removed from the patient to a desired target previously programmed into the system. When low-water-transmission cellulosic membranes are employed, negative pressure must be generated on the dialysate side of the membrane by the machine in order to accomplish sufficient water removal. Because suction may be applied to the dialysate as it transits the dialyzer, it must first be placed under a greater vacuum in a degassing chamber so that air bubbles are not generated within the dialyzer that would cause errors in the calculation of ultrafiltration by the sensors and also reduce the efficiency of the dialyzer. On the other hand, when high-water-transmission, synthetic membranes are used, it is frequently necessary to apply positive pressure on the dialysate side to control the otherwise excessive rate of ultrafiltration.
The majority of dialyzers are reused in the United States. The trend worldwide is towards reusing dialyzers. There are numerous procedures for reusing dialyzers both manually and automatically. In centers, special machines for simultaneous multiple dialyzer reprocessing are used.
These procedures must be conducted in a biohazard environment since there is always the potential for exposure to human blood, and hepatitis and AIDS are relatively prevalent in the dialysis population. Also, the OSHA and EPA stipulate various working environment regulations owing to the hazardous sterilizants and cleaning agents used.
Reprocessing of dialyzers and lines may be performed on the dialysis machine. The Boag patent, U.S. Pat. No. 4,695,385, discloses a cleaning apparatus for dialyzer and lines. The device is permanently or semipermanently connected into the dialysis machine system.
Finally, the dialysis machine fluid circuits must be periodically cleaned and disinfected. There are two reasons for this. The first relates to the fact that the dialysate has historically not been sterile. From the very beginning of dialysis as a therapy, the dialyzer membrane has been relied upon to be a sterile barrier between dialysate and blood. This is certainly true for whole bacteria, but concern has been growing over the past several years that with the use of synthetic membranes and their more porous structure, endotoxins, or components thereof, may by permeating these membranes and activating inflammatory processes within the patients. When dialysate containing bicarbonate is used, calcium carbonate inevitably precipitats and accumulates on the plumbing and must be dissolved with an acidic solution.
Historically, many artificial kidneys have utilized a proportioning system for producing dialysis solution and delivering it into a hemodialyzer. In the early years of hemodialysis only a so-called tank or batch system was used. The machine was provided with a large tank where purified water was premixed with dry chemicals to make dialysis solution, which was warmed and recirculated through the dialyzer dialysate path. Bicarbonate was used as a buffer; CO.sub.2 was bubbled through the solution, or lactic acid was added to the solution to prevent calcium/magnesium carbonate precipitation. With inefficient dialyzers, a dialysis time of 12 hours or more was used. Warm dialysate was an excellent culture medium for bacterial growth. Long dialysis treatment time magnified the problem. To overcome this problem a proportioning system was designed whereby the solution was being prepared ex tempore from purified water and concentrate. The concentrate contained acetate as the physiologic buffering agent because bicarbonate tended to precipitate with calcium and magnesium if present in the same concentrate.
As of the mid-1990's there are approximately 180,000 patients on dialysis in the United States, almost 500,000 worldwide. Most of them dialyze in hemodialysis centers and approximately 17% are on home peritoneal dialysis with less than 3% on home hemodialysis. Typically, in-center hemodialysis is performed three times per week for between two and four hours. The more physiologically desirable four times per week dialysis sessions are used only with patients with severe intolerance to three times weekly dialysis, generally due to cardiovascular instability. Home hemodialysis is also typically performed three times weekly.
Three dialysis sessions per week is considered a standard schedule in the majority of dialysis centers, yet there is considerable scientific evidence that more frequent dialysis for shorter periods of time is more beneficial. Whereas the normal human kidneys function continuously to produce gradual changes in total body fluid volume and metabolic waste levels, three times weekly dialysis schedules produce abnormal physiological fluctuations which yield considerable stress on the patient's systems.
The amount of time consumed travelling to and from the center, and the dialysis procedure itself, is mostly tolerable for the patients who perform three sessions per week. Consequently, only those patients who experience unbearable intolerance of body fluid volume fluctuations, and the associated symptoms, agree to more frequent (four times weekly) dialysis sessions. For home dialysis patients, more frequent dialysis than three times per week would mean more stress on the relatives who help with set-up and who monitor the patient and on the patient who does most of the work for set-up, tear-down, and cleaning. Accordingly, the use of home hemodialysis on a frequent basis (four or more times per week) has, at least heretofore, not been widely practiced.
Many patients have enormous difficulties achieving a "dry" body weight if they accumulate three, four, or more kilograms of fluid between dialysis treatments. Some patients, especially those with heart disease, poorly tolerate even a two kilogram fluid weight gain; they are short of breath before dialysis, have muscle cramps and hypotension during dialysis, and feel "washed out" and are extremely weak, needing several hours to "equilibrate" and become functional. Serum concentration of highly toxic potassium frequently reaches dangerous levels (more than seven mEq/L), particularly preceding the first dialysis after a longer interval (weekend). To mention only a few others, calcium and pH are too low before dialysis or too high after dialysis in many patients. Empirically, in many hemodialysis units, these patients are placed on a four times weekly dialysis schedule.
Historically, artificial kidney systems were developed according to the assumption that the machine should be very sophisticated and automated during dialysis and less so for preparation and cleansing. This assumption was valid for long and infrequent dialysis sessions where compared to the total dialysis time the time for setup and cleansing of the machines was relatively short.
More efficient dialyzers were eventually designed, and time of a single dialysis session gradually decreased to 8, 6, 5, 4, 3, and even 2 hours. With very efficient dialyzers, acetate was delivered to the patient in excess of the body ability to metabolize it, which caused cardiovascular instability. An answer to this problem was to return to bicarbonate as a buffer but within an overall design of proportioning system. Because of chemical incompatibility of bicarbonate with calcium and magnesium, two proportioning pumps are required, the first to mix the bicarbonate concentrate with water and the second to proportion this mixture with the concentrated electrolytes to achieve the final, chemically compatible solution. However, a short daily dialysis session of 1-3 hours offers a possibility of abandoning the proportioning system.
If short daily hemodialysis is done in a dialysis clinic, the travel time, inconvenience and expense incurred by the patient increases dramatically. If such a practice is adopted by a large number of the center's patients, the staff at the treatment center is also burdened. Additionally, the dialysis facility's capacity for performing this number of incremental treatments would have to be increased, requiring capital expansion. Consequently, the patient's home is a desirable location for this treatment modality.
U.S. Pat. No. 5,336,165 to Twardowski describes techniques for overcoming many of the problems associated with conventional dialysis devices. This patent describes a hemodialysis system which has a built-in water treatment system; automatic formulation of batch dialysis solution; automated reuse; automated set-up; automated cleaning and disinfection of blood and dialysate circuits; and reduction in storage space by utilizing dry and concentrated chemical reagents. This system is suitable for home dialysis.
The failure of home hemodialysis to achieve the widespread popularity is due partly to the failure in the art to produce a user-friendly, efficient, and affordable home hemodialysis system that relieves the patient and the patient's family from time-consuming and tedious pre-treatment and post-treatment set-up and teardown of the home hemodialysis equipment. The present inventive machine remedies this situation, offering patients a hemodialysis system particularly suitable for short daily hemodialysis in the home environment.
The present invention relates to a modular hemodialysis machine especially suitable for use in the home environment that provides for a cost-effective, transportable, simple and highly reliable home hemodialysis system that automates substantially the entire process and requires a minimum of patient input and labor. By substantially reducing the labor intensity and disposables cost associated with prior art home hemodialysis treatment equipment, the present invention is intended to open up the availability of short daily hemodialysis in the home environment to a larger pool of hemodialysis patients. These patients, by practicing the present invention, can avail themselves of this treatment modality, which has proven to yield outstanding clinical benefits, without having the inconvenience of travel to remote treatment centers.